深层煤上储层地震描述技术——以永进油田西山窑组为例

Seismic description technology of deep reservoirs above coal seams:a case study of Xishanyao formation in Yongjin Oilfield

在油气勘探中,煤层的存在会对之上或之下的储层产生影响,给储层精确描述带来困难.永进油田西山窑组主力油层下方存在多套煤层,严重影响了储层的精细刻画.从正演模拟可以看出：1）煤层的强反射压制了储层同相轴,使储层呈弱反射特征;2）对合成地震记录做广义S变换（GST）,煤层形成的GST谱能量团＂亮点＂叠置在目的层上,将储层的有效信息掩盖.分析实际资料还可以看出,该区存在目的层埋藏深（6000 m左右）、单层薄（最大8 m）,主频低（约25 Hz）等难点.基于此,先利用匹配追踪技术进行煤层剥离,其中最佳匹配控制参数通过井旁道去煤层试验获取,对于本区相位选择范围为-2～0,尺度因子取0.95为好;再利用GST较高的时频分辨率特性,对有效信息集中在18～36 Hz频谱成分的目的层,在时频域进行分频重构.实际资料处理后,剖面及谱的能量团＂亮点＂能很好地对应储层,砂体反演的纵向厚度及横向分布范围与井点吻合度提高,GST分频重构则进一步凸显了本区储层特征.研究对深化永进油田及西部类似区块的储层认识,有积极的参考作用.

In the oil and gas exploration,the coal seams have an impact on reservoir above or below it,which brings difficult to accurate description of reservoir. The presence of interbeded coal seams at Xishanyao formation in Yongjin oilfield seriously affects the precise characterization of reservoir. It can be seen from the forward modeling： 1） The strong reflection of coal seams suppresses the event of reservoir, which results in the weak reflection characteristics. 2） After using generalized S transform（ GST） for synthetic seismogram,we can see that the ＂ bright spot ＂ of GST spectral energy group formed by coal seams is stacked on the target layer,which shields the useful information of reservoir. There still exist some problems in this area,such as target layer buried deep（ 6000 meters）,single-layer thin（ max 8 m）,and lower main frequency（ about 25 Hz）. Based on those, matching pursuit technology is used to remove coal seams in this paper. The best match control parameters can be determined by the experiment of removing coal seams at up-hole trace. In this area,the range of phase is from-2 to 0,and the scaling factor is 0. 95. Then,the useful information of target layer which centralized from 18 to 36 Hz spectral components is reconstructed in time-frequency domain using GST. After the process of the real data,energy group ＂ bright spots＂ in seismic profile can better correspond to reservoir and the vertical thickness and horizontal distribution of sand body inversion can better conform to the well. The GST frequency-divided reconstruction can highlight the feature of the reservoir furtherly in this area. This study has positive reference for deepening understanding of reservoir in Yongjin oilfield and other west similar projects.